The investigators propose a multicenter prospective trial to assess the accuracy of Positron Emission Tomography (PET) performed with the tracer 2-(18-F)- fluoro-2-deoxy-D-glucose (FDG) in staging patients with newly diagnosed breast carcinoma. Their study will also determine the prognostic value of information derived from the initial PET scans as an indicator of disease-free survival. Three clinical sites will contribute patients to the study: the University of Michigan Medical Center (Ann Arbor, MI); Washington University Medical Center (St. Louis, MO); and Duke University Medical Center (Durham, NC). Data management will be provided by the American College of Radiology Clinical Trials Division. Study design and interim and final data analyses will be coordinated by the principal investigator and investigators from the Harvard Medical School. The mechanism they propose for conduct of this study closely parallels that used successfully in several other prospective evaluations of imaging methods in cancer. The following scientific assessments will be performed: (1) The accuracy of PET for the detection of axillary nodal metastasis of breast cancer will be determined. Disease status will be proven by axillary nodal dissection with careful histological examination of the removed axillary lymph nodes. This will be accomplished by studying 138 women at each of the three performance sites over a 30-month acquisition period. The total number of patients to be studied among the three centers during the data-acquisition phase will be 414. (2) The prognostic value of information derived from the initial PET staging procedure as an indicator of disease-free survival or recurrence will be determined. This will be achieved during a follow-up observation period after patient accrual is completed. In this follow-up phase, bone scans (386/performance site) will be obtained at yearly intervals as well as careful physical examinations and routine blood chemistry studies. They will ascertain whether PET staging of breast cancer offers a similar or greater level of prognostic information for predicting disease-free survival than do standard invasive staging methods. Through this multicenter trial, they expect to have sufficient patient accrual to define (1) the accuracy of FDG PET in staging nodal metastases of breast carcinoma and (2) the capability of FDG PET for stratifying patient risk of recurrent disease at the time of initial presentation. Such data are essential for determining the role of PET in the diagnostic algorithm of patients with newly diagnosed primary breast cancer and in determining whether a single noninvasive PET study can replace axillary dissection in the staging of such patients. Successful noninvasive assessment of nodal status and prognosis by FDG PET would represent the next important step beyond lumpectomy in minimizing patient disfigurement, allowing for increasingly noninvasive therapy of breast cancer.